Production of high vacuum



Aug. 9, 1938. P. v. MALLOY 2,126,686

PRODUCTION QF HIGH VACUUM Filed Feb. 11, 1956 FIG. 3

ATTORNEY Patented Aug. 9, 1938 PATENT OFFICE PRODUCTION OF HIGH VACUUM Paul V. Malloy, Lakewood, Ohio, assignor to Kemet Laboratories Company, Inc., a corporation of New York Application February 11, 1936, Serial No. 63,302

1 Claim.

The invention relates to the production of high vacuum and provides new and useful method and means for producing a high vacuum within a closed envelope such as that of a thermionic valve or similar device.

One common procedure for evacuating a thermionic device involves two steps: The major part of the gas is exhausted by pumping and the remainder is cleaned up by vaporizing within the device a small amount of anactive material, or getter, usually a metal or alloy comprising metals of the alkali, alkaline earth, and rare earth metal groups, and which combines avidly with gas. It has been the practice to secure a small piece or tablet of getter material within a depression provided in a thin strip of metal, to fasten the strip within the outer glass envelope of the thermionic device, and to induce electric currents in the strip from. a coil outside the envelope, whereby the getter is heated and vaporized, or flashed.

The procedure described above has been used successfully for the production of many millions of thermionic valves. Nevertheless, it possesses certain limitations. The time required to flash the getter is at least four to six seconds, for if sufficient power is used in the induction coil to speed up the flashing step, the getter material tends to blow out of its support with a small explosion, to splash on the valve elements, to drop unvaporized particles of getter into the envelope, and to form a poorly adherent film of metal on the glass envelope. The slowness of the flashing step not only limits the output of the evacuating machine, it also tends to heat the metal elements and nonmetallic insulators of the valve excessively and unevenly, tending at times to warp and to weaken them.

It is an object of the present invention to eliminate the above described limitations to the use of .getters. This and other objects are attained by so arranging the getter and its support that, as the support is inductively heated, successive portions of the getter are vaporized. Thus, the getter is vaporized smoothly and steadily from the beginning to the end of the support-heating period instead of suddenly and explosively at the end of that period.

A typical embodiment of the invention is illustrated in the accompanying drawing in which:

Fig. 1 is a plan view of a getter and getter support.

Fig. 2 is a cross-sectional view taken through 2-2 of the device shown in Figure 1, and

Fig. 3 is a front elevation, partly in cross-section, of a thermionic valve and the device shown in Figures 1 and 2, arranged for the flashing operation.

Referring specifically to Figures 1 and 2, the device shown therein consists of a single thin 5 strip ID of metal, which is preferably nickel, provided with an elongated pocket I l which extends from the outer edges of the strip to its central portion. A body l2 of active getter material'is contained within the pocket II and is preferably in firm contact with the metal strip I 0. The outer ends of the.pocket H are preferably sealed by bending over the ends to form ears M or by an equivalent expedient. One side of the strip is preferably bent to form a wing l3 which acts to direct the vapors of getter material during flashing.

In Figure 3 is shown a typical way of using the device illustrated in Figures 1 and 2. The strip of metal l0 containing the active getter is suspended below the operating elements l5 and within the outer envelope l6 of a thermionic device. High frequency electric current is passed through a coil 11 placed about the envelope l6 at the level of the strip l0. Currents are induced in the strip l0 and heat it, the outer edges being heated first and the heat then proceeding progressively towards the center of the strip. Thus, portions of the active getter l2 near the outer edge of the strip 10 are vaporized almost immediately and portions progressively nearer the center are vaporized as they are raised progressively to a high temperature. The total time for flashing is thereby considerably reduced, from five or six seconds to about 2 seconds for instance, a consistently effective clean-up action is obtained, and the film of getter deposited on the wall of the envelope is securely adherent.

It is preferred that the pocket ll be formed in the strip I0 by bending and folding the strip, rather than by drawing it. By bending closed the entrance of the pocket II, and by bending flaps [4 at the ends of the pocket, there is formed a sheath which will spring open sufliciently to permit the escape of vapors but insufliciently to allow particles of metal or cinder to drop out of the pocket.

Although it is preferred that the active material I2 be retained in the strip III by means of the pocket ll, other means of fastening the active material along a line extending from the center to one or more edges of the strip are within the invention. For instance, a strip or small bar of active material may be welded or otherwise adhesively secured in place on the strip l0. firm thermal contact with said strip, said body I claim: extending substantially from the edge to the cen- Method of producing a high vacuum within a ter portion of said strip, and then heating said closed envelope which comprises securing below strip from its edges progressively towards its censaid operating elements within said envelope ter, whereby Successive p rtions of said getter 5 containing the operating elements of a therat are po e mionic device; a getter tab consisting of a metal PAUL V. MALLOY. strip and a body of getter material secured in CERTIFICATE OF OORREOTION.

Patent No. 2,126,686., n August 9-, 193

PAUL v. iLALLOY. 7

It is hereby certified that error appears in the printed specification I of the above mnnbered'pete'nt requiring correction as follows: Page 2, first column, line 1 claim 1, after "envelope insert the words containing the operating elements of'a thermionic device; and lines 6 and 7, same claim,

strike out the words end semicolon "containing. the operating elements of a thermionic 'device;; and that the said Letters Patent shouldbe readwith this correction therein that the same may conform to the-record of the case in the Patent Office Signed and sealed this hth day of October, A, D. 1938.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

